Electrodeposition of iron and neodymium from calcium chloride hexahydrate eutectic solvents

High water content type IV-deep eutectic solvents (DES) formed from calcium chloride hexahydrate and ethylene glycol (CaCl 2 ⋅6H 2 O:EG) were investigated for the deposition and co-deposition of Fe, Nd and FeNd. Cyclic voltammetry demonstrated the feasibility of electrodepositing of Fe, Nd and FeNd, despite the DES containing ca. 21.3 mol kg ‒1 water. Diffusion coefficients for the soluble Fe 2+ and Nd 3+ species were estimated using the Cottrell equation to be in the order of 10 –7 to 10 –6 cm 2 s −1 at 40°C. A coating of pure Fe was observed under insonated conditions. Whereas, the electrodeposition of Nd was unaffected by the presence of ultrasound, suggesting that it is not solely limited by mass transport or the development of a stable passivation layer. A significant proportion of oxygen and carbon was detected in the Nd deposit, indicating the likely presence of solid Nd glycolate species, along with Nd oxides or hydroxides formed upon exposure to air. Co-deposition of Fe and Nd under silent conditions resulted in a deposit containing an atomic% ratio of 1.7:1 Fe:Nd. Under insonation conditions, the electrodeposition of Fe was significantly enhanced with a much higher ratio of 126:1 Fe:Nd. The Scharifker-Hills model revealed that the electrodeposition of Fe and FeNd occurred by instantaneous nucleation, while Nd followed progressive nucleation indicating that the electrodeposition of the two species occurs inhomogeneously. This study shows the solvent CaCl 2 ·6H 2 O:EG has the potential to be applied to the electrodeposition of other reactive elements.